The present invention relates to a jig for welding pipe ends. More particularly this invention concerns this invention concerns a device that fits inside a pair of pipe ends to be welded together and that holds them coaxial during the welding operation, normally while flooding the joint from inside with an inert gas.
When a pair of pipe ends are to be welded coaxially together it is standard to use a jig that comprises a pair of parts that are fitted into the aligned pipe ends and then expanded radially. The pipe ends and jig parts are then fitted together so that the pipe ends are aligned perfectly coaxially and solidly held during the welding operation. Such a device as defined in the KWU product literature xe2x80x9cPiping Systemsxe2x80x9d (July 1985).
This device is relatively complex to use and is quite expensive. It has a hydraulic actuator for spreading the two pairs of wedges and locking it in place, and involves separate pieces that must be installed separately. It is difficult to use and therefore takes considerable setup time.
It is therefore an object of the present invention to provide an improved pipe-end jig.
Another object is the provision of such an improved pipe-end jig which overcomes the above-given disadvantages, that is which is of simple construction and that is easy to use.
A jig for coaxially welding together a pair of generally coaxial tubular pipe ends meeting at a joint has according to the invention a pair of support bodies in the pipe ends flanking the joint and each having an outer surface tapering axially inward toward the joint. Respective arrays of wedges are axially displaceable on the surfaces so that as the arrays are displaced apart the respective wedges move radially outward. Respective springs engaging the arrays urge the respective jaws radially together and urge the respective arrays axially toward each other. An abutment between the arrays has annular end faces engageable axially outward with the respective wedges. thus when the bodies are drawn axially toward each other and the respective wedges are forced radially outward so that when the arrays are flanking a joint and displaced radially outward they coaxially center and lock together the pipe ends.
Thus with this system the two bodies are moved apart to bring the wedges inward so the jig can be fitted between two juxtaposed pipe ends. The bodies are them moved together to press the wedges against inner surfaces of the pipe ends and lock them coaxially together. Even if the two pipe ends are not of identical diameter, they will be coaxially centered and fixed relative to each other. After the jig is tightened to align the pipe ends, these ends can be welded together by conventional inert-gas welding or another process. Thereafter the bodies are moved together and the jig is pulled axially out of the joint.
According to the invention the abutment is formed with a pair of axially oppositely extending guides on which the respective bodies are axially slidable. These guides are axially extending tubes and the bodies are formed with axially inwardly open annular grooves complementarily receiving the respective guides.
The abutment according to the invention is formed by a pair of axially joined disks each having an axially extending outer flange forming the respective end face. It is formed with at least one radially outwardly open passage through which an inert gas can be fed into a space defined between the arrays and within the pipe ends at the joint. A fine-pore diffuser covers an outer end of the passage.
The wedges in accordance with the invention are formed with radially outwardly open seats. The springs are annular and engaged in the seats of the respective arrays. In a system for use in curved pipes, the wedges have inner edge portions and outer edge portions and the inner edge portions extend radially outward farther than the respective outer edge portions.
Each body is formed at an inner end of the respective frustoconical surface with a radially outwardly projecting stop lip. In addition the drawing-together means comprises an outer tube connected to one of the bodies, an inner element connected to the other of the bodies, and means for relatively shifting the outer tube and inner element. The tube and inner element can be rigid or flexible.